Rotation-detecting apparatus

ABSTRACT

A rotation-detecting apparatus includes the following: a rotor coil provided on a rotor; detection coils provided on stators; a control circuit that detects the relative rotational angle between the rotor and the stators by processing detection signals induced in the detection coils as a result of the rotor coil being excited by an excitation signal; and a communicating means for performing data communication with an external device. The control circuit in the rotation-detecting apparatus has functionality whereby a switch signal that turns on and off at preset rotational angles is outputted on the basis of the aforementioned detection signals. Also, the control circuit is designed such that the set rotational angles for the aforementioned switch signal can be changed by the external device via the abovementioned communicating means.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This is a National Stage Entry into the United States Patent andTrademark Office from International PCT Patent Application No.PCT/JP2014/072169, having an international filing date of Aug. 25, 2014,the entire contents of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a rotation-detecting apparatus capableof detecting the relative angle of rotation between a rotor and astator.

BACKGROUND OF THE INVENTION

In related art, a mechanical cam has been used in manufacturingfacilities in many fields. The mechanical cam is so configured that adisk-shaped cam is directly connected to a rotating body undermeasurement and a contact piece that is in contact with the cam providesa predetermined timing signal (switch signal) that follows the shape ofthe cam. The mechanical cam, however, is prone to wear of the cam andpositional shift thereof, and cumbersome work, such as cam reproductionprocessing and position adjustment, is therefore required.

On the other hand, for example, Japanese Patent Laid-Open PatentApplication No. 2007-76672 employs an electronic method, so to speak,using a resolver and a variable cam switch attached to the rotatingshaft to provide the switch signal described above. That is, theresolver outputs predetermined reference voltage to the variable camswitch, and the variable cam switch outputs a switch signal according tothe angle of rotation (rotational position) of the rotating shaft to acontrol apparatus (control panel) that serves as a high-level apparatus.

SUMMARY OF THE INVENTION

The method using the resolver and the variable cam switch, however, alsorequires a space for accommodating the resolver and the variable camswitch and causes the number of parts to be increased and the costassociated with the accommodation work to be added. In this regard, itis conceivable to carry out the process of generating the switch signalin the high-level apparatus without using the variable cam switch orother components. In this case, however, it is conceivable that somesystems cause a problem if the switch signal is not produced when meansfor communication (such as network) with the rotation-detectingapparatus malfunctions or the high-level apparatus fails.

The present invention has been made in view of the circumstancesdescribed above, and an object of the present invention is to provide arotation-detecting apparatus capable of not only reducing the overallsize of the rotation-detecting apparatus but also enhancing reliability.

A rotation-detecting apparatus includes a rotor and stators, a rotorcoil disposed in the rotor, detection coils disposed in each of thestators, a control circuit that processes detection signals induced inthe detection coils when the rotor coil is excited with an excitationsignal to detect a relative angle of rotation between the rotor and thestators, and communication means for data communication with an externalapparatus, wherein the control circuit has a function of outputting aswitch signal that turns on and off at a preset angle of rotation basedon the detection signals and is configured to allow the externalapparatus to change a setting of the angle of rotation associated withthe switch signal via the communication means.

In the invention, since the rotation-detecting apparatus can detect therelative angle of rotation between the rotor and the stators on thebasis of the detection signals induced in the detection coils, unlikewith a mechanical cam, the problems such as wear of the cam andpositional shift can be solved. Further, since the rotation-detectingapparatus incorporates the control circuit and outputs the switch signaldescribed above, the overall size of the rotation-detecting apparatuscan be reduced. Moreover, not only can the switch signal be outputtedindependently of the external apparatus, but also the external apparatusis allowed to change the setting of the angle of rotation associatedwith the switch signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment and is a block diagram showing the electricalconfiguration of a rotation-detecting apparatus.

FIG. 2 is an enlarged longitudinal cross-sectional view showing aportion including a rotor substrate and stator substrates.

FIG. 3 is an exploded view of multilayer substrates that form the rotorsubstrate and the stator substrates.

FIGS. 4(a) and 4(b) are conceptual views for describing the positionalrelationship between a rotor coil and a stator coil associated with a 1Tsensor section.

FIG. 5 is a diagram corresponding to FIG. 4 but shows the positionalrelationship in a 16T sensor section.

FIG. 6 is a block diagram associated with a computation process.

FIG. 7 is a conceptual view for describing digital position signals fromthe 1T sensor section and the 16T sensor section.

FIG. 8 shows the relationship between the frequency of an excitationsignal and a detection signal (output voltage) in the rotation-detectingapparatus.

FIG. 9 describes the difference in characteristics between two-sidestators and a one-side stator in the 1T sensor section, FIG. 9(a)showing the relationship between the amount of shift of the rotorsubstrate and the output voltage, and FIG. 9(b) showing the relationshipbetween the amount of shift of the rotor substrate and a detection angleerror.

FIG. 10 corresponds to FIG. 9 and shows the 16T sensor section.

FIG. 11 describes a constant current drive method.

FIG. 12 describes a pulse encoder function.

DESCRIPTION OF EMBODIMENT(S) OF THE INVENTION

An embodiment of a rotation-detecting apparatus 10 according to thepresent disclosure that is used in an FA (factory automation) fieldnetwork will be described below with reference to the drawings. In theblock diagram of FIG. 1, an outer shell case 10 b and a rotating shaft10 a of the rotation-detecting apparatus 10 are diagrammatically shownfor ease of description. The rotation-detecting apparatus 10 includes astator provided in the outer shell case 10 b and a rotor provided aspart of a shaft 10 a, which is a sensor shaft, and the stator and therotor are formed of a stator substrate 11 having detection coils 21 aand 21 b, which will be described later, and a rotor substrate 12 havinga rotor coil 22, as shown in FIG. 1.

The stator substrate 11 is further provided with an excitation coil 14.For example, when a single-phase AC signal is inputted as apredetermined excitation signal to the excitation coil 14, the rotorcoil 22 is excited. When the rotor coil 22 is excited, a sine-wave phaseoutput signal and a cosine-wave phase output signal having undergoneamplitude modulation in accordance with the rotation of the shaft 10 aare induced in the detection coils 21 a and 21 b. The sine wave sin θand the cosine wave cos θ are used to determine tan θ, which is thenused to determine arctangent to carry out the process of computing anangle of rotation θ of the shaft 10 a. As described above, therotation-detecting apparatus 10 according to the present embodiment isbased on single-phase-excitation/dual-phase-output amplitude modulationby way of example. It is noted thatdual-phase-excitation/single-phase-output, that is, inputting AC signalshaving the same amplitude but different phases to the excitation-sidetwo phases allows the rotation-detecting apparatus 10 to be used inphase modulation in which the phase of an output signal changes inproportion to the angle of rotation θ.

In the rotation-detecting apparatus 10, the stator substrate 11 and therotor substrate 12, which are described above and serve as a sensorsection, and a detection circuit substrate 15, on which a controlcircuit that controls the stator substrate 11 and the rotor substrate 12is mounted, are accommodated in the single case 10 b, as shown inFIG. 1. A controller 17 is mounted on the detection circuit substrate 15disposed in the case 10 b. The controller 17 is a control circuitformed, for example, of a microcomputer, an FPGA (Field ProgrammableGate Array), a DSP (Digital Signal Processor), and other components,controls the entire detector 10, carries out the computation processdescribed above, and performs other types of operation.

Output signals from the detection coils 21 a and 21 b are inputted tothe controller 17 described above via a sensor interface (I/F) 16. Aninternal power supply circuit 18, a network I/F 19, a memory section 20,and a contact output circuit 23 are connected to the controller 17. Theinternal power supply circuit 18 supplies each circuit in therotation-detecting apparatus 10 with electric power supplied from anexternal power supply external to the rotation-detecting apparatus 10with the electric power transformed and stabilized as required.

The network I/F 19 is communication means connected, for example, to aPLC (Programmable Logic Controller) as a high-level unit that is notshown via a control-system network. Specifically, in a case where therotation-detecting apparatus 10 is used as one of a variety ofmeasurement/control apparatus in in-factory manufacturing facilities,the signals processed by the controller 17 are transmitted from thenetwork I/F (field bus I/F) 19 via a field bus 19 a to the PLC describedabove. As described above, in the present embodiment, a variety ofmeasurement/control apparatus, such as the rotation-detecting apparatus10, are used as field apparatus, and the field bus 19 a connects thefiled apparatus to the high-level field apparatus (PLC, for example) viaa single cable. The thus configured field network allows digitization ofsignals, common use of wiring, and other types of operation forreduction in the number of wiring lines and cost. The field networkfurther allows the standards of the field apparatus to be made clear sothat the connection and maintenance of the field apparatus can bereadily performed and a variety of apparatus are allowed to operate onthe field bus 19 a. The field network can, for example, begeneral-purpose Ethernet (registered trademark) and may be configured asnot only a closed network that is not supposed to be connected toanother network but also a network in a broad sense (including closednetworks connected to one another).

The field apparatus described above can be systemized withoutconsideration of protocols and other factors by providing each of thefield apparatus with a communication CPU that is, for example, adedicated chip that is supplied from the manufacturer of the fieldapparatus and carries out a communication process over the fieldnetwork. In this case, however, the dedicated chip increases the cost(price of the dedicated chip as a component is added), the chip occupiesa large mounting space on the detection circuit substrate 15, and otherproblems arise. In the present embodiment, to allow the controller 17 tohave the function of the dedicated chip, a process program stored in thememory section 20 is executed to carry out the process of communicatingwith the high-level field apparatus and other apparatus, a communicationprocess relating to compatibility among application programs, and otherprocesses. Instead, the hardware configuration of the FPGA (gate array)described above and other components or software configuration is usedto omit the dedicated chip but achieve the function thereof. Therotation-detecting apparatus 10 can thus achieve reduction in the sizeand cost of the internal substrate 15. Further, integration of thesensor section described above with the detection circuit therefor inconjunction with use of the field network allows the entire footprintincluding the wiring described above to be minimized to construct ahighly rational system.

The memory section 20 described above includes a nonvolatile memory,such as a ROM, a volatile memory, such as a RAM, and an electricallyrewritable nonvolatile memory, such as an EEPROM. The memory section 20stores the process program described above and other programs. Thememory section 20 may also store in advance a correction value forimproving rotational position/output value linearity. Further, as willbe described later in detail, in the present embodiment, forming therotor coil 22 in a waveform shape (see coils 221 to 224 and 221 h to 224h in FIG. 3) allows improvement in the linearity without use of anycorrection value.

The number of contacts of the contact output circuit 23 described aboveis set as appropriate in accordance with the space required to mount thecontact output circuit 23 and as required. The contact output circuit 23has the function as an electronic cam that outputs a digitized signalrepresenting, for example, ON and OFF and forms, along with thecontroller 17 described above, a control circuit. The electronic cam isconfigured to refer to the angle of rotation θ as absolute data to turnon and off a cam switch signal (output signal) corresponding to an angleset by a user. In this regard, in the case of a cam limit switch, whichis formed of a mechanical cam, ON/OFF timing setting requires cumbersomework, such as adjustment of the positions of the components of the camlimit switch. On the other hand, in the case of an electronic cam, thesetting can be more readily performed by the user's input operation.Specifically, data points (angles) relating to the ON/OFF timing areset, for example, by the high-level field apparatus or a dedicatedapparatus (either of them is assumed to be an external apparatus) at theuser's desired value via the field bus 19 a (over network). For example,when angles of rotation θ of 0 degrees (first angle) and 90 degrees(second angle) in terms of mechanical angle are set by input operationperformed on the external apparatus, the controller 17, when itdetermines that the angle of rotation θ of the shaft 10 a is greaterthan or equal to 0 degrees but smaller than or equal to 90 degrees,turns on (or off) the output signal for the period for which the angleof rotation θ falls within the range from 0 degrees to 90 degrees. In acase where the set values remain unchanged, a simple state in whichthere is no connection to the network can be achieved, or default valuesthat are the first and second angles can be stored in advance in theEEPROM or any other device in the memory section 20 and can be updatedby changing the set default values. Further, an electronic cam isadvantageous in terms of maintenance because wear or positional shift ofthe cam and other problems therewith do not occur, unlike a mechanicalcam.

The cam switch signal does not need to respond at high speed dependingon the application of the electronic cam, and the high-level fieldapparatus can process the signal. In this case, the high-level fieldapparatus reads the binary data via the field bus 19 a and outputs thecam switch signal. However, for example, it is conceivable that somesystems cause a problem if the cam switch signal is not produced whenthe network malfunctions or the high-level field apparatus fails.Further, in some applications of an electronic cam, a delay period fromthe point of time when the angle of the shaft 10 a changes to the pointof time when the cam switch signal is produced is required to be smallerthan or equal to several dozen microseconds, that is, required to beresponsive at high speed. In this case, turning on and off the outputsignal after the high-level field apparatus reads the data results in along delay period and cannot therefore satisfy the requirement describedabove. It is therefore very significant to perform high-speed ON/OFFcontrol independently, for example, of the network.

In this regard, the rotation-detecting apparatus 10 incorporates thesensor section, the controller 17, the contact output circuit 23, andother components and has a variety of functions including the functionof an electronic cam. Further, the controller 17 can be formed not onlyof the FPGA but also of a dedicated gate array to allow electronic camON/OFF control. Further, as will be described later in detail, settingthe excitation signal to oscillate at a high frequency ranging from 100KHz to 5 MHz allows the data update period, that is, the delay perioddescribed above to be set, for example, at 10 μs or shorter, whereby therequirement of a high-speed response of the electronic cam can besatisfied. The contact output circuit 23 may be configured to have thefunction of a pulse encoder that will be described later.

Further, the contact output circuit 23 has a speed limit detectionfunction of outputting a switch signal that turns on and off inaccordance, for example, with a result of comparison between the angleof rotation θ described above (or the number of rotations, which will bedescribed later) per predetermined period and a predetermined threshold.The speed limit detection function is the function of turning on or offthe output signal when the rotational speed of the shaft 10 a is greaterthan or equal to the predetermined threshold, which serves as areference (speed limit guideline), and the function can be set in avariety of manners by the external apparatus described above.

In detail, the controller 17 computes the angle of rotation θ per thepredetermined period, which is measured by using a clock signalgenerated by a quartz oscillator provided in the controller 17, that is,the rotational speed [rpm] of the shaft 10 a. Further, as will bedescribed later in detail, the controller 17 identifies the direction ofthe rotation of the shaft 10 a by using the absolute data and generatesa rotation direction identification signal. The memory section 20 storesclockwise (CW) and counterclockwise (CCW) default values set as thepredetermined threshold. The predetermined threshold can be set at aplurality of different values desired by the user's input operationperformed on the external apparatus described above irrespective of thedirection of the rotation or in each of the directions of the rotation,and the thus changed predetermined threshold is stored in the memorysection 20. Therefore, for example, in a case where the lower value andthe higher value of the plurality of predetermined thresholds set forthe clockwise (CW) rotational speed are called a first threshold and asecond threshold, respectively, the controller 17 turns on (or off) theoutput signal when the computed rotational speed is determined to begreater than the first threshold in the clockwise (CW) rotationaldirection and turns off (or on) the output signal when the computedrotational speed is determined to be greater than the second threshold.

In contrast to the present embodiment, there is a speed switch thatmechanically opens and closes the switch. For example, in acentrifugal-force-based speed switch, a movable portion that moves basedon centrifugal force is accommodated in an enclosure that forms an outershell of the switch, and the switch is configured to open and close anelectric contact in accordance with a change in the position of themovable portion due to the rotation of the shaft of the movable portion.In this configuration, the rotational speed at the time when theelectric contact opens or closes is determined in a physical sense, andthe direction of the rotation of the shaft cannot be identified.Further, the centrifugal-force-based speed switch is not allowed tochange the threshold in accordance with which the electric contact opensor closes or cannot have a plurality of thresholds. The mechanicalmovable portion causes unstable detection of the rotational speed andabnormal action due, for example, to wear, rust, and dust. Further, theenclosure of the speed switch requires a space for ensuring the movablerange of the movable portion and stable action thereof, and it istherefore difficult to achieve size reduction.

In this regard, in the present embodiment, the controller 17 producesthe absolute data, as described above, which allows, in conjunction withthe quick response of the detection signal and the precise clock signal,the rotational speed to be calculated in an extremely simple, precisemanner. Further, a plurality of thresholds of the rotational speed canbe set by the external apparatus via the field bus 19 a in each of therotational directions. In a case where the set thresholds remainunchanged, the rotation-detecting apparatus 10 can be disconnected fromthe network. Therefore, even if communication malfunction occurs in thenetwork, the speed limit detection function (contact output) of therotation-detecting apparatus 10 normally operates, and no wear problemor no abnormal action problem occurs, unlike in related art, whereby areliable system can be constructed.

Multilayer Substrate

The outer shell case 10 b of the rotation-detecting apparatus 10 has,for example, a cylindrical shape, and the stator substrate 11 and therotor substrate 12, each of which has, for example, a disc-like shape,are disposed in the case 10 b. The stator substrate 11 is formed of apair of stator substrates, which are attached to the outer shell case 10b at upper and lower two locations therein in FIG. 2. The pair of statorsubstrates 11 are formed of substrates having roughly the sameconfigurations and disposed symmetrically on the upper and lower sides.Therefore, in the following description, the upper substrate has areference character “11 u”, the lower substrate has a referencecharacter “11 d”, and components of the substrates collectively have thesame reference characters.

Each of the stator substrates 11 u and 11 d is formed of ageneral-purpose printed multilayer substrate formed, for example, of afirst layer L1 to a third layer L3. Each of the stator substrates 11 uand 11 d has a through hole 110 provided in a central portion thereofand having a diameter larger than the diameter of the shaft 10 a and isso disposed that the shaft 10 a is inserted into the through hole. Aninsulating material of each of the stator substrates 11 u and 11 d is,for example, a four-layer glass-based epoxy resin. In the exploded viewof the stator substrates 11 u and 11 d shown in FIG. 3, a coil patternlayer is provided in each of the first layer L1 and the second layer L2,and a wiring layer is provided in the third layer L3. Further, in eachof the stator substrates 11 u and 11 d, the coil pattern layers areelectrically connected to the wiring layer by what is called throughhole drilling.

Specifically, in each of the stator substrates 11 u and 11 d, the coilpattern layer on the first layer L1 is formed by a planar copper-foilpattern and formed of an excitation coil 141 on the inner circumferenceside and detection coils 211 a, 211 b, 211 ah, and 211 bh on the outercircumference side. Among the coils, the detection coils 211 a and 211b, which are inner-circumference-side coils, each correspond to a1-pitch coil, which will be described later, and are coils for detectingthe absolute position of the shaft 10 a over 360 degrees in terms ofmechanical angle (angle in a case where one rotation of the shaft 10 acorresponds to 360 degrees). The detection coils 211 ah and 211 bh,which are outer-circumference-side coils, each correspond to a 16-pitchcoil, which will be described later, and are coils for detecting theangle of rotation at high resolution.

Similarly, the coil pattern layer in the second layer L2 is formed of anexcitation coil 142 on the inner circumference side and detection coils212 a, 212 b, 212 ah, and 212 bh on the outer circumference side. Anexcitation coil 14 in each of the stator substrates 11 u and 11 d isformed of the patterned excitation coils 141 and 142, which form aplurality of layers. Detection coils 21 a and 21 b in each of the statorsubstrates 11 u and 11 d are formed of the patterned coils 211 a to 212bh, which form a plurality of layers.

The wiring layer in the third layer L3 is formed of pattern minute linesthat link terminals p1, p2, . . . , that form a group terminal P shownin FIG. 3 to each other for wiring purposes. The stator substrates 11 uand 11 d face the rotor substrate 12 with gaps therebetween in such away that the first layer L1 is located on the inner side and theterminal group P in the third layer L3 is located on the outer side withrespect to the rotor substrate 12, as shown in FIG. 2. Each of thestator substrates 11 u and 11 d does not necessarily have theconfiguration described above, and the configuration described above maybe changed as appropriate, for example, an electromagnetic waveshielding layer is provided between the second layer L2 and the thirdlayer L3.

The rotor substrate 12 described above is formed of a general-purposeprinted multilayer substrate formed, for example, of a first layer L1 toa fourth layer L4, and a glass-based epoxy resin is used as aninsulating material. The rotor substrate 12 has a fitting hole 111provided in a central portion, and the shaft 10 a is fit into thefitting hole 111 so that the rotor substrate 12 is attached and fixed tothe shaft 10 a. Each of the first layer L1 to the fourth layer L4 of therotor substrate 12 has a planar coil pattern layer formed of a copperfoil and serving as the rotor coil 22.

Specifically, transformer coils 241 and 244, which correspond to theexcitation coils 141 and 142 in the stator substrates 11 u and 11 d, areprovided in the first layer L1 and the fourth layer L4 of the rotorsubstrate 12 and on the inner circumference side thereof, as shown inFIG. 3. An excitation signal (AC signal) is supplied from the excitationcoils 141 and 142 in the stator substrates 11 u and 11 d to thetransformer coils 241 and 244 in the rotor substrate 12 in a noncontactmanner. The coils 141, 142, 221, and 224 form a rotary transformer.

Inner-circumference-side one-pitch coils 221, 222, 223, and 224, whichare electrically connected to the transformer coils 241 and 244, andouter-circumference-side 16-pitch coils 221 h, 222 h, 223 h, and 224 h,which are also electrically connected to the transformer coils 241 and244, are provided in the first layer L1 to the fourth layer L4 of therotor substrate 12. The 1-pitch coils 221 to 224 and the 16-pitch coils221 h to 224 h are formed in the positions corresponding to thedetection coils 211 a to 212 b and 211 ah to 212 bh in the statorsubstrates 11 u and 11 d.

As described above, forming the stator and the rotor in the form of themultilayer substrates 11 u, 11 d, and 12 allows elimination of assemblyof components to a magnetic material in related art, whereby the numberof manufacturing steps can be reduced for cost reduction. Further,abrupt change in magnetic characteristics due to saturation of themagnetic material does not occur, and the amount of influence of biasdue to an external magnetic field and temporal change therein can bereduced. Each of the multilayer substrates 11 u, 11 d, and 12 is lighterthan a substrate made of a magnetic material so that the weight of thesubstrate can be greatly reduced, whereby load inertia can be minimized.In particular, in a case where the rotation-detecting apparatus 10 isused, for example, in a servo motor, the rotation-detecting apparatus 10contributes to no useless load inertia in the view of the motor, wherebythe rotation-detecting apparatus 10 is practically useful. Further, themultilayer substrates 11 u, 11 d, and 12 allow coil patterns having avariety of shapes to be readily produced with a small amount ofmanufacturing variation, unlike a winding using a magnet wire.

Pitch and Shape of Coil

Each of the 1-pitch coils 221 to 224 and the 16-pitch coils 221 h to 224h in the present embodiment has a sinusoidal shape. In FIGS. 3 to 5, thesinusoidal shape of each of the coils 221 to 224 and 221 h to 224 h isconceptually replaced with a rectangular waveform for ease ofdescription. FIG. 4 schematically shows the positional relationshipbetween the 1-pitch coil 221 and the detection coils 211 a and 211 b,and FIG. 5 schematically shows the positional relationship between the16-pitch coil 221 h and the detection coils 211 ah and 211 bh.

That is, the 1-pitch coil 221 shown in FIG. 4(a) actually has asinusoidal shape that extends along an annular shape (extending incircumferential direction of rotor substrate 12) (see FIG. 3), and 1pitch corresponds to 360 degrees (one rotation) in terms of mechanicalangle. The pair of detection coils 211 a and 211 b shown in FIG. 4(b)are positioned so as to be shifted from each other by the ¼ pitches andprovided in alternation. In FIGS. 4(a) and 4(b), each of the coils 221,211 a, and 211 b actually arranged in an annular shape is shown in adeveloped form that extends in the rightward/leftward direction.

The electromagnetic coupling between the 1-pitch coil 221 and thedetection coils 211 a, 211 b, that is, the voltage induced, is maximizedin a position where the coil 221 overlaps with the coil 211 a or 211 b.The induced voltage gradually decreases as the rotor substrate 12 movesin the rotational direction thereof (see the rightward arrow in FIG.4(a)) and becomes 0 in the position where the coils are shifted fromeach other by ¼ pitches so that the magnetic fluxes produced by thecoils cancel each other. The induced voltage then has maximized but hasa reverse polarity in the position where the coils are shifted from eachother by ½ pitches, and when the rotor substrate 12 further rotates, theinduced voltage becomes 0 again in the position where the coils areshifted from each other by ¾ pitch. Thereafter, in the position afterthe movement corresponding to 1 pitch, the maximum induced voltage isprovided again. The thus changing induced voltage draws a 1-cycle linethat completes in the cycle of rotation of the rotor substrate 12, whichis equal to 1 pitch of the coil 221, and the cycle of the inducedvoltage repeats afterward in the same cycle as the rotor substrate 12rotates.

In the detection coils 211 a and 211 b shown in FIG. 4(b), which areshifted from each other by ¼ pitches, are generated two types of inducedvoltage resulting from the electromagnetic coupling that changes andfollows cosine and sine curves as the rotor substrate 12 rotates. Thethus changing degree of electrical coupling in the detection coil 211 ais proportional to cos θ, where θ is the difference in relative position(relative angle) between the rotor substrate 12 and the statorsubstrates 11, whereas the degree of electrical coupling in thedetection coil 211 b is proportional to sin θ. Therefore, since thechange in the two types of induced voltage is unambiguously correlatedto the relative angle between the 1-pitch coil 221 and the two coils 211a, 211 b, the angle of rotation can be determined by detection of thevoltage induced in each of the detection coils 211 a and 211 b.

The 16-pitch coil 221 h shown in FIG. 5(a) also has a sinusoidal shapethat actually extends along an annular shape (see FIG. 3), and FIG. 5(a)conceptually shows part of the coil 221 h. The number of pitches α of16-pitch coil 221 h in the rotor substrate 12 is 16, that is, one pitchcorresponds to the angle corresponding to 1/16 rotations (22.5 degrees)in terms of mechanical angle. The term “1 pitch” used herein correspondsto a segment where an absolute position is detected within the angularrange of the “1 pitch”. The number of pitches, which is the number ofdivided segments, is not limited to “16” and can be changed asappropriate, for example, can be set at “8” or “32”.

One of the detection coils 211 ah and 211 bh shown in FIG. 5(b), in thiscase the coil 211 bh, is shifted from the 16-pitch coil 221 h by ¼pitches. Further, since the detection coils 211 ah and 211 bh areshifted from each other by ¼ pitches, induced voltage proportional tocos(αθ) is sensed in the detection coil 211 ah, and induced voltageproportional to sin(αθ) is sensed in the detection coil 211 bh.

Conceptual View of Signal Processing

FIG. 6 is a conceptual view of signal processing in the controller 17 ofthe rotation-detecting apparatus 10 described above. Reference characterθ denotes the angle of rotation of the rotor substrate 12, which rotatesalong with the shaft 10 a, and l cos wt in FIG. 6 denotes the excitationsignal (MHz-band AC current that will be described later) supplied tothe excitation coils 141 and 142. The 1-pitch coils 221 to 224 and the16-pitch coils 221 h to 224 h are excited via the transformer coils 241and 244 (rotary transformer). At this point, a sine-wave phase outputsignal and a cosine-wave phase output signal having undergone amplitudemodulation in accordance with the rotation of the shaft 10 a are inducedin the detection coils 21 a and 21 b.

An output signal (Kp·cos ωt·cos 16θ) from the detection coils 211 ah and212 ah for the 16-pitch coils is inputted to a synchronous rectifiercircuit 31 shown in FIG. 6. An output signal (Kc·cos ωt·cos θ) from thedetection coils 211 a and 212 a for the 1-pitch coils is inputted to asynchronous rectifier circuit 32. An output signal (Kc·cos ωt·sin θ)from the detection coils 211 b and 212 b for the 1-pitch coils isinputted to a synchronous rectifier circuit 33. An output signal (Kp·cosωt·sin 16θ) from the detection coils 211 bh and 212 bh for the 16-pitchcoils is inputted to a synchronous rectifier circuit 34. The referencecharacters 1, Kp, and Kc are coefficients, and the following referencecharacters Lp and Lc are also coefficients.

The synchronous rectifier circuits 31 to 34 perform synchronousrectification of the respective output signals. Lowpass filters (LPFs)35 to 38 remove high-frequency components from the respective outputsignals from the synchronous rectifier circuits 31 to 34. A computationcircuit 39 a then computes the angle of rotation θ on the basis of asignal inputted from the lowpass filter 35 (Lp·cos 16θ) and a signalinputted from the low pass filter 38 (Lp·sin 16θ). A computation circuit39 b computes the angle of rotation θ on the basis of a signal inputtedfrom the lowpass filter 36 (Lc·cos θ) and a signal inputted from the lowpass filter 37 (Lc·sin θ). A computation circuit 40 then combines thevalues calculated by the computation circuits 39 a and 39 b with eachother to detect the angle of rotation θ of the shaft 10 a as theabsolute data that will be described below and provides the angle θ athigher resolution.

1T Sensor Section and 16T Sensor Section

The angle of rotation θ described above is given in the form of a 4-bitdigital position signal in association with the 1-pitch coils 221 to 224and in the form of a 16-bit digital position signal in association withthe 16-pitch coils 221 h to 224 h. FIG. 7 shows values of the digitalposition signal associated with the 1-pitch coils 221 to 224 and thedetection coils 211 a to 212 b (hereinafter referred to as 1T sensorsection) and the digital position signal associated with the 16-pitchcoils 221 h to 224 h and the detection coils 211 ah to 212 bh(hereinafter referred to as 16T sensor section).

As shown in the same figure, when the shaft 10 a rotates by 360 degreesin terms of mechanical angle, the 1T sensor section provides a digitalvalue ranging from “0” to “15”, and the 16T sensor section provides adigital value that repeatedly increments from “0” to “4095” 16 times.The 1T sensor section and the 16T sensor section have roughly the samenonlinearity of the outputs signals therefrom over one pitch, that is,roughly the same ratio of linearity error associated with the angle ofrotation. Therefore, in the view of the mechanical angle of the shaft 10a, the 16T sensor section can reduce the degree of error by a factor of16 as compared with the degree of error in the 1T sensor section, whichis preferable from the viewpoint of error characteristics. Similarly,the 16T sensor section is more preferable also in terms of resolution(the number of divided segments described above), temperaturecharacteristics, and noise resistance characteristics.

As described above, the 16T sensor section, which has relatively finerpitch, is effective as means for improving the sensor characteristics,but the range over which the angle of rotation can be detected as anabsolute value, that is, the 1-pitch mechanical angle is limited to 22.5degrees. The 16T sensor section cannot therefore detect the rotationalposition of the shaft 10 a over 360-degree mechanical angle or cannotidentify one out of the 16 blocks shown in FIG. 7. On the other hand,the 1T sensor section is inferior to the 16T sensor in terms of avariety of characteristics but has 1 pitch corresponding to 360 degreesin terms of mechanical angle and can therefore detect the rotationalposition of the shaft 10 a over one rotation. Therefore, the positionalsignal from the 1T sensor section is used to identify the blockposition, which is unknown by the 16T sensor section. As describedabove, in the case of the data configuration shown in FIG. 7, therotation-detecting apparatus 10 detects, as a one-rotation absolutesensor, a change in rotation of 360 degrees/(4096×16) in terms ofmechanical angle.

The 1T sensor section and the 16T sensor section are therefore used toperform simultaneous detection to allow absolute sensing of one rotationof the shaft 10 a with high precision and by using a large number ofdivided segments. The 16T sensor section may instead have an 8T pitch (⅛division) or a 32T pitch ( 1/32 division). The number of dividedsegments is set in accordance with the physical coil arrangement spaceand the number of bits based on which the 1T sensor section identifiesthe rotational position. Further, the sensor sections are notnecessarily the two sensor sections, 1T and 16T, and a multilayersubstrate that incorporates three sensor sections, for example, 1T, 8T,and 64T, or four or more sensor sections may be used for higherperformance. The multilayer substrates 11 u, 11 d, and 12 describedabove allow high design flexibility including coil formation and simple,easy implementation of a plurality of various coils (sensor sections),whereby an inexpensive configuration is achieved.

Frequency of Excitation Signal

In a rotation sensor, such as an inductosyn (product name), to increasethe inductance and the degree of magnetic coupling of a sensor coil, thestator and the rotor are typically made of a metal material, such asiron, as the magnetic material. The frequency of the excitation signalin such a rotation sensor is set at a value ranging from about severalhundred Hz to 10 KHz. The reason for this is as follows:

(1) Since the inductance is sufficiently high, even arelatively-low-frequency excitation signal can provide an adequatedetection signal.

(2) Unlike the present embodiment, a rotation sensor is separate from adetection circuit (control apparatus) therefor. Therefore, since therotation sensor and the control apparatus are separate from each otherby a separation distance (length of cable that connects them to eachother), the frequency is set at a low value so that the inter-linecapacity does not affect the detection signal. Further, inter-linecrosstalk degrades the sensor linearity, and the degree of influence ofthe crosstalk on the sensor linearity changes with the length of thecable.

(3) Since the inductance is high, as described in [1], a high-frequencyexcitation signal is affected by resonance, which increases an error.

(4) An iron steel plate or silicon-containing steel plate used as themagnetic material does not provide very good high-frequencycharacteristics.

(5) Even in a case where a rotation sensor is used in a servo system, anexcitation signal having a frequency of about 20 KHz practicallysuffices.

(6) In an analog system, intended characteristics cannot be achieved inhigh-speed operation.

On the other hand, assume that no magnetic material is used, as in thepresent embodiment, and that a multilayer substrate including coils isaccommodated in the case 10 b, for example, having a diameter of about60 mm. In this case, the diameter of the multilayer substrate is about50 mm, and the inductance value of the coils (sensor section) in theview of an excitation circuit is a very small, for example, a valueranging from several to 10 μH. Assuming now, for example, that theinductance is 10 μH and the frequency is 10 KHz, impedance Z1 is asfollows:Z1=2πfL=2π×10×10³×10×10⁻⁶≅0.63[Ω]  (1)

In this regard, output current of about 0.5 [A0-P] from a sensor drivecircuit that excites the coils is not technically difficult to achieveas long as a strong buffer circuit is employed. However, such a circuitundesirably causes not only an increase in the number of parts, anincrease in current consumption, and other problems but also anotherproblem, such as a decrease in reliability due to heat generation.Further, providing a heatsink increases the footprint, which contradictsthe technical idea of size reduction resulting from integration of thesensor section with the control apparatus, which is the technical ideaof the present embodiment. In view of the facts described above, theoutput current from the sensor drive circuit is set at a value rangingfrom about 10 to 30 [mA0-P]. For example, when drive current of 30[mA0-P] is applied to Z1 in Expression (1) (≅0.63Ω), voltage V1 acrossthe sensor section is as follows:V1=Z1×30≅18.8 [mV_(0-P)]  (2)

It is noted that a DC resistance component is neglected in Expression(2).

Further, detection voltage V2 induced in a secondary detection circuit,that is, on the secondary side in the sensor section is believed to beapproximately several percent of the voltage V1 described above. Asdescribed above, in the present embodiment, in which the degree ofmagnetic coupling cannot be increased, unlike a typical configuration inwhich a magnetic material is used, the ratio of the detection voltage V2to the voltage V1 is taken into consideration. For example, when theratio is 3%, the detection voltage V2 is as follows:V2=V1×0.03=18.8×0.03≅0.56 [mV_(0-P)]  (3)

The result shows that when the sensor section is excited with anexcitation signal having a frequency of 10 [KHz] and a drive current of30 [mA0-P], the detection voltage is 0.56 [mV0 -P]. In this regard,although the detection voltage is amplified or otherwise processed andeventually inputted to an A/D converter, the input voltage typicallyneeds to be about several volts.

The detection voltage therefore needs to be amplified by a factor of atleast 3000 under this condition, and the gain needs to be increasedaccordingly, resulting in an increase in the number of parts. Further,unintended positive feedback is applied in some cases to anamplification circuit having a very high gain due to slight couplingbetween the signal input stage and the amplified signal output stage(electrostatic coupling, magnetic coupling, and common impedance),resulting in oscillation of the circuit. Above all, the detectionvoltage itself is small, so that noise from the amplification circuititself and external noise undesirably tend to affect the detectionsignal.

Briefly consider now the noise from an amplifier. A first-stageoperational amplifier that amplifies the detection voltage V2 needs tohave a sufficiently wide bandwidth including the operation frequency sothat no phase shift occurs in the 10 [KHz]-signal. In this regard, sincethe input-equivalent noise voltage density of a typical widebandoperational amplifier is about 10 nV/(Hz)½, input section noise voltageVn is as follows when the bandwidth described above is set at 1 [MHz]:Vn=10×10⁻⁹×(1×10⁶)^(1/2)=0.01 [mV_(0-P)]  (4)

Vn is about 2% of V2=0.56 [mV0-P] in Expression (3) and seeminglyappears not to be a big problem. In a configuration for achieving higherdetection precision, however, ultralow-input use condition, in whichnoise inputted to a first-stage operational amplifier affects thedetection signal, is practically very problematic. Further, in additionto the external noise described above, noise from a power supply line inthe circuit, switching noise from a DC/DC power supply, crosstalk from alogic signal, and other types of noise affect the signal.

As measures to be taken against the problems described above, it isconceivable to increase the magnitude of the excitation signal current,but this is not preferable from the reason described above. In view ofthe facts described above, in the present embodiment, the frequency ofthe excitation signal is increased. For example, when the frequency ofthe excitation signal is increased from the original 10 KHz by a factorof 10 to 100 KHz, Z1, V1, and V2 described above are as follows:Z1=2πfL=2π×100×10³×10×10⁻⁶≅6.3[Ω]  (5)V1=Z1×30≅188 [mV_(0-P)]  (6)V2=188×0.03≅5.6 [mV_(0-P)]  (7)

As described above, the detection voltage V2 is increased in proportionto the frequency of the excitation signal, and the noise resistanceincreases accordingly. Therefore, when the frequency of the excitationsignal is further increased by a factor of another 10 to 1 MHz, thedetection voltage V2 is also more preferably increased by a factor ofanother 10. Further, the problems [2] to [6] described above in the casewhere the frequency of the excitation signal is set at a large value canbe solved as follows:

Problem [2]

Since the sensor sections and the detection circuit including thecontroller 17 are accommodated in the same case 10 b, which is the caseof the rotation-detecting apparatus 10 according to the presentembodiment, the length of the cable between the rotor substrate 12 andthe detection circuit substrate 15 can be minimized. The length of thecable in this case can be shortened to a minimized fixed length (shorterthan or equal to 3 cm, for example). The inter-line capacitance of thecable therefore affects the detection signal only by a substantiallynegligible amount. In other words, it can be said that increasing thefrequency of the excitation signal and arranging the sensor sections andthe control device therefor close to each other are compatible with eachother.

Problems [3] and [4]

The rotation-detecting apparatus 10 has low inductance because nomagnetic material is used, and the frequency of the excitation signal istherefore set at a relatively large value. This is tied closely to theproblem of degradation in high frequency characteristics of a stator anda rotor made of a magnetic material. By the way, it is known that thereason why a resonance state (self-resonance) occurs in a typicalinductance part having excellent frequency characteristics, such as acommercially available choke coil, is that the impedance of theinductance part ranges from about one to several ten kilo-ohms. In thiscase, irrespective of the inductance value, resonance occurs at afrequency that causes the impedance to range from about one to severalten kilo-ohms. It is therefore believed that resonance occurs due to aphysical limitation set by a coil and the inter-line capacity of thecoil itself.

Resonance similarly occurs in the rotation-detecting apparatus 10according to the present embodiment from the viewpoint of inductance,and to avoid influence of a current phase unsteady state due to theresonance phenomenon, the rotation-detecting apparatus 10 should bedriven at a frequency sufficiently lower than the resonance frequency.It is therefore believed that the rotation-detecting apparatus 10satisfactorily functions as a sensor without being affected by theresonance as long as the impedance value is smaller than or equal to avalue ranging from about several ten kilo-ohms to several hundred ohms.The frequency is now back calculated from Z1 described above in a casewhere the limit of the impedance is set, for example, at 300Ω asfollows:f=Z1/2πL≅4.8 [MHz]  (8)

That is, the frequency that allows the rotation-detecting apparatus 10to satisfactorily function without being affected by the resonance isabout 5 MHz in principle. It is noted that since the design of each ofthe coils in the sensor sections is flexible to some extent, the valuedescribed above is not altogether the absolute limit. Further, in a casewhere the impedance is too high, driving the rotation-detectingapparatus 10, for example, by current having the magnitude of 30 [mA0-P]undesirably causes too much increase in the voltage across the coil, andthe rotation-detecting apparatus 10 cannot be driven in an intendedmanner. In this regard as well, it is reasonable to set the frequency ofthe excitation signal to fall within a range that allows the impedanceof the coil to be lower than or equal to several hundred ohms.

Problem [5]

As described above, in the present embodiment, since the frequency ofthe excitation signal is set in a range greater than the range inrelated art, the response frequency associated with the rotationalposition detection can be improved. It can therefore be said that theconfiguration in the present embodiment is a preferable configuration.

Problem [6]

As semiconductor devices advance in recent years, an operationalamplifier, which is important in the detection circuit in the presentembodiment, having a band higher than 1 GHz and being compact andinexpensive is readily available. Further, an A/D converter, which isalso important in the detection circuit, having a sampling rate higherthan 100 MHz and being compact and inexpensive is readily available.Under these circumstances, in the rotation-detecting apparatus 10 usingthe parts described above, the present inventor has constructed adetection circuit that operates at an excitation signal frequency of 5MHz.

FIG. 8 shows the relationship between the frequency of the excitationsignal supplied to the excitation coils 141, 142 and the voltage V2detected at the detection coils 211 ah to 212 bh (detection value inrotor position where voltage V2 is maximized). As shown in FIG. 8, whenthe frequency of the excitation signal is 10 KHz, 100 KHz, 1 MHz, and 5MHz, the peak value [mV0-P] of the detection voltage V2 is about 0.06,0.85, 21.2, and 115, respectively. It can therefore be verified that thedetection voltage V2 increases roughly in proportional to the frequencyof the excitation signal and increases to sufficiently large values at 1MHz and 5 MHz. It is noted that the reason why such high frequencieshave not been set in related art is believed to no necessity to set thefrequency at a high value in the first place (current state at the pastpoint of time sufficed) and no attempt to improve the detection voltage.

As described above, in the present embodiment, it is recommended thatthe frequency of the excitation signal be set at a high frequency higherthan or equal to 100 KHz, preferably at a value ranging from 100 KHz to5 MHz, more preferably at a value ranging from 1 MHz to 5 MHz. As aresult, even the rotation-detecting apparatus 10 using no magneticmaterial is allowed to have synergistically enhanced sensorcharacteristics, an improved response frequency, and other advantageouseffects that have not been achieved in related art.

Shape of Rotor Coil

When each of the coils 221 to 224 h in the rotor substrate 12 has asinusoidal shape, intended induced voltage can be achieved even when thepitches of the coils including the detection coils 211 a to 211 bh andthe distances between the substrates 11 u, 11 d, and 12 are arbitrarilyset. That is, in the multilayer substrates 11 u, 11 d, and 12, aprecise, special coil pattern that cannot be achieved by using a wiringusing a magnet wire as in related art can be formed in a patternformation process.

In this regard, a typical inductosyn (product name) has a rectangularwaveform coil, but in a case where the dimensional shape described above(case 10 b having diameter of 60 mm) is applied to an inductosyn, it hasbeen demonstrated that the linearity of output variation characteristicdeteriorates. To avoid the situation, setting appropriate distancesbetween the rotor substrate 12 and the stator substrates 11 u, 11 d (seeGu and Gd in FIG. 2), which will be described later, and designing acoil shape according to a coil configuration suitable for performancemaintenance (1T and 16T sensor sections) allow improvement in thelinearity without no increase in material cost or the number ofmanufacturing steps.

It is also possible to employ a configuration in which the memorysection 20 described above stores detection errors for each of the 1Tand 16T sensor sections and the angle of rotation θ is computed by usingthe detection errors as correction values. In this configuration,however, an increase in cost due to a correction process carried out foreach of the sensor sections and other downsides are conceivable.Therefore, forming each of the coils 221 to 224 h in a sinusoidal shape,as in the present embodiment, allows improvement in the linearity in asimple configuration with no correction of the angle of rotation θ. Itis noted that even when each of the coils 221 to 224 h is formed in asinusoidal shape, an error correction process may be so carried out thatthe amount of error is reduced as much as possible.

Arrangement and “Shift” of Substrates

The present inventor has conducted an experiment in which the currentconfiguration of the rotation-detecting apparatus 10 is compared with aconfiguration without one of the stator substrates or the statorsubstrate 11 u (upper substrate 11 u in FIG. 2) in order to verify theadvantageous effects provided by the two stator substrates 11 u and 11d, which sandwich the rotor substrate 12. In the following description,the former configuration is abbreviated to two-side stators 11 u, 11 d,and the latter configuration is abbreviated to one-side stator 11 d.FIG. 9 shows a result of the experiment using the 1T sensor section inwhich 1 pitch corresponds to 360 degrees in terms of mechanical angle,and FIG. 10 shows a result of the experiment using the 16T sensorsection in which 1 pitch corresponds to 22.5 degrees in terms ofmechanical angle.

The distances Gu, Gd between counterposed surfaces of the two-sidestators 11 u, 11 d and the rotor substrate 12 in FIG. 2 are each set at0.35 mm, and the horizontal axis in FIGS. 9 and 10 represents the amountof axial shift of the rotor substrate 12 (upward in axial direction isassumed to be positive in FIG. 2). In FIGS. 9(a) and 10(a), currentapplied by a primary signal (excitation signal) associated with the 1Tand 16T sensor sections is set at 30 [mA0-P], which is close to anactual value, and peak voltages [mV0-P] of a secondary signal (outputvoltage) V2 resulting from the primary signal are shown.

In the 1T sensor section shown in FIG. 9(a), the difference in themagnitude of the output voltage V2 between the two-side stators 11 u, 11d and the one-side stator 11 d is obvious, and the ratio between thevoltage values from the two types of stator is about 3.6 in the casewhere the rotor substrate 12 is located in the original referenceposition (0 mm). Also in the 16T sensor section shown in FIG. 10(a),FIG. 10(a) show a large difference in the magnitude of the outputvoltage V2 between the two-side stators 11 u, 11 d and the one-sidestator 11 d, and the voltage ratio is about 3.7 in the case where therotor substrate 12 is located in the reference position. Further, ineach of the 1T and 16T sensor sections, the two-side stators 11 u, 11 dhas a small amount of influence on the output voltage V2 even if therotor substrate 12 is shifted from the reference position by ±0.3 mm, asshown in FIGS. 9(a) and 10(a). In contrast, the one-side stator 11 dcauses the output voltage V2 to decrease as the rotor substrate 12 movesaway from the reference position. Therefore, a secondary output voltageratio representing the ratio of the output voltage V2 provided by thetwo-side stators 11 u, 11 d to the output voltage V2 provided by theone-side stator 11 d shows large differences between the two types ofstator, that is, the ratio is 6.3 in the 1T sensor section (see FIG.9(a)), and the ratio is 7.6 in the 16T sensor section (see FIG. 10(a)).As a result, it is found that the two-side stators 11 u, 11 d canprovide output voltage V2 much greater than that provided by theone-side stator 11 d, whereby decrease in the voltage can be suppressedand the performance can therefore be maintained even if the substrates11 u, 11 d, and 12 are shifted from each other when they are assembledto each other or due to use over time.

Further, in the 1T sensor section, the amount of shift of the rotorsubstrate 12 from the reference position is roughly proportional to thedetection error of the angle of rotation θ due to the shift, as shown inFIG. 9(b). In this case, the detection error that occurs in the two-sidestators 11 u, 11 d is much smaller the detection error that occurs inthe one-side stator 11 d, that is, smaller than or equal to ⅕ thereof.Also in the 16T sensor section in FIG. 10(b), when the rotor substrate12 is shifted from the reference position, the detection error thatoccurs in the two-side stators 11 u, 11 d falls within a range smallerthan or equal to ¼ of the detection error that occurs in the one-sidestator 11 d. The result shows that even if the substrates 11 u, 11 d,and 12 are shifted from each other when they are assembled to each otheror due to use over time, the two-side stators 11 u, 11 d allow thedetection precision to be maintained with the detection error minimized,and it can be said that the two-side stators 11 u, 11 d is insensitiveto the axial shift.

Phase of Excitation Current

In the rotation-detecting apparatus 10, consider the process ofdetecting the output signals induced in the detection coils 21 a and 21b by driving the excitation coils 141 and 142 to excite the rotor coil22 via the rotary transformer. In this case, the phase of the voltagethat is the output signal from each of the detection coils 21 a and 22 bcoincides with the phase of the current flowing through the excitationcoils 141 and 142.

That is, first of all, since the input impedance of the detectioncircuit is designed to be sufficiently higher than the impedance of eachof the detection coils 21 a and 22 b, the phase does not change at theinput of the detection circuit. On the other hand, when the coils 141and 142 on the excitation side are voltage driven, the “phase ofcurrent” flowing through each of the coils 141 and 142 is determined bythe impedance of the coil. The impedance is the combination of the“resistance” component and the “inductance-induced reactance” componentof each of the coils 141 and 142 (see FIG. 11(b)). In the case of thecoils 141 and 142 in the multilayer substrates 11 u and 11 d, theresistance value is not so small that it is negligible relative to theinductance value. That is, the current flowing through each of the coils141 and 142 does not have a waveform in which the phase is delayed by 90degrees with respect to the phase of the drive voltage across thecorresponding one of the coils 141 and 142, unlike in the case of anideal inductor having negligible resistance component.

Unlike the present embodiment, in a system using a typicalrotation-detecting apparatus, means for synchronously rectifying adetection signal by using an excitation signal as a reference signal isemployed. In the synchronous rectification process, the relationshipbetween the phase of the reference signal and the phase of the detectionsignal is also important information for detecting the angle of rotationθ, and in the case where the phase shift occurs as described above, itis conceivable that the problem described above is solved by offset ofthe phase of the reference signal by a necessary amount. In this case,however, when a change in the temperature around the sensor sectionchanges the resistance component of the coil (see ΔR in FIG. 11(b)), thephase of the excitation current is shifted accordingly. The shiftedphase directly results in a shift of the phase of the voltage in thedetection circuit. As a result, a shift occurs in data on the angle ofrotation θ.

To avoid the situation described above, in the rotation-detectingapparatus 10 according to the present embodiment, the coils 141 and 142on the excitation side are driven by a constant current drive circuit50, which supplies the coils 141 and 142 with fixed drive current, asshown in FIG. 11(a). Therefore, even if a change in the temperature inthe surroundings changes the resistance components of the coils 141 and142, the change can be compensated by the constant current driveperformed on the coils 141 and 142 (constant current control performedby controller 17), and the phase of the excitation current can behandled as a known value. The correction associated with a temperaturechange can also be achieved by constant voltage drive. The temperaturecorrection can instead be made by using a counter that counts time untila zero-cross point is reached to detect the phase of the excitationcurrent flowing through each of the excitation coils 141 and 142,whereas the constant current drive described above allows the detectionprecision to be improved in a simple configuration that does not requirethe detection circuit described above.

Pulse Encoder Function

The contact output circuit 23 in the rotation-detecting apparatus 10 canbe equipped with, in addition to the electronic cam function and thespeed limit detection function described above, the function as a pulseencoder by using the absolute data. A pulse encoder is a device thatoutputs phase-A, phase-B, and phase-Z pulse signals from the contactoutput circuit 23. Among the outputted pulse signals, the phase-Z signalis formed of pulses representing the reference position outputtedwhenever the encoder makes one rotation. In the following description, amethod for producing the phase-A and phase-B pulses is brieflydescribed.

The controller 17 described above outputs the digital position signalfrom the 1T sensor section or the 16T sensor section, as sensor data, toa difference computation circuit 51, as shown in FIG. 12(a). Thedifference computation circuit 51 reads the sensor data in constantcycles, computes a difference between the sensor data in the currentcycle and the sensor data in the preceding cycle, and outputs thedifference to a downstream pulse conversion circuit 52. The differencecomputation circuit 51 further identifies the direction of the rotationof the shaft 10 a on the basis of the computed difference and outputs arotational direction identification signal to a pulse generation circuit53.

The pulse conversion circuit 52 converts the inputted difference intouniform pulses that are uniform over a constant cycle, as shown in FIG.12(b). The pulse generation circuit 53 then generates the phase-A pulsesignal on the basis of the inputted uniform pulses and rotationaldirection identification signal and further generates the phase-B pulsesignal that is delayed by ¼ cycle with respect to the phase-A pulsesignal. The number of pulses in each of the phase-A and phase-B pulsesignals, that is, the pulse rate that is the ratio between the amount ofrotation and the number of generated pulses is assumed to be set at anarbitrary value by an external setting operation section (not shown)from which the arbitrary value is inputted via the field bus 19 adescribed above.

Unlike the configuration described above, in a typical pulse encoderusing an optical sensor, in which a disk-shaped glass plate directlyconnected to a shaft is used, the glass plate could be broken whenimpact acts thereon. Further, a light emitting device and a lightreceiving device based on optics each have a relatively short life andkeep deteriorating due to heat. Therefore, pulses may not be outputtedor the duty ratio of the pulses may change from 50% in some cases.Further, when condensation occurs on an optical portion or dust or anyother foreign matter intrudes, malfunction immediately occurs, theencoder itself cannot be used, and other problems occur.

In this regard, the rotation-detecting apparatus 10 according to thepresent embodiment, which uses no optical sensor of related art, isallowed to function as a pulse encoder that outputs the phase-A,phase-B, and phase-Z pulse signals on the basis of the absolute data.The rotation-detecting apparatus 10 therefore excels in durability andhas a prolonged life or can solve the problems described above. Further,the rotation-detecting apparatus 10 is configured to be capable ofchanging the setting of the pulse rate on the basis of a setting valueinputted from the setting operation section described above. Therefore,a variety of manufacturing facility reserve parts on a pulse rate basisare not required to be prepared, unlike in related art, and therotation-detecting apparatus 10 therefore excels in versatility.

As described above, the rotation-detecting apparatus 10 according to thepresent embodiment includes the rotor coil 22, which is disposed in therotor, the detection coils 21 a and 21 b, which are disposed in each ofthe stators, the control circuit (controller 17 and contact outputcircuit 23) that processes the detection signals induced in thedetection coils 21 a, 21 b when the rotor coil 22 is excited with theexcitation signal to detect the relative angle of rotation between therotor and the stators, and the communication means for datacommunication with an external apparatus. The control circuit has thefunction of outputting a switch signal that turns on and off at a presetangle of rotation on the basis of the detection signals, and the controlcircuit is configured to allow the external apparatus to change thesetting of the angle of rotation associated with the switch signal viathe communication means.

Since the thus configured rotation-detecting apparatus 10 can detect therelative angle of rotation between the rotor and the stators on thebasis of the detection signals induced in the detection coils 21 a and21 b, unlike with a mechanical cam, the problems such as wear of the camand positional shift, can be solved. Further, since therotation-detecting apparatus incorporates the control circuit andoutputs the switch signal, the overall size of the rotation-detectingapparatus can be reduced. Moreover, not only can the switch signal beoutputted independently of the external apparatus, but also the externalapparatus is allowed to change the setting of the angle of rotationassociated with the switch signal.

Further, the control circuit described above has the speed limitdetection function of measuring the angle of rotation per apredetermined period on the basis of the detection signals andoutputting a switch signal that turns on and off in accordance with aresult of comparison between the measured angle of rotation and apredetermined threshold, and the control circuit is configured to allowthe external apparatus to change the setting of the predeterminedthreshold associated with the measured angle of rotation per thepredetermined period via the communication means.

The thus configured rotation-detecting apparatus 10 requires no movableportion or other components, for example, in the conventionalcentrifugal-force-based speed switch described above can be omitted,whereby the problem of abnormal action can be solved. Further, since thecontrol circuit is built in the rotation-detecting apparatus, aconfiguration generally suitable for overall size reduction can beachieved. Moreover, not only can the switch signal be outputtedindependently of the external apparatus, but also the external apparatusis allowed to change the setting of the predetermined thresholdassociated with the measured angle of rotation per the predeterminedperiod.

Each of the rotor and the stators may instead be formed of a platemember made of a magnetic material in place of the multilayer substrates12, 11 u, and 11 d described above. Further, the frequency of theexcitation signal is not limited to the high frequency described aboveand may be changed as appropriate in accordance with the material of theplate member.

In any case, accommodating the substrates that form the rotor, thestators, and the control circuit in the single outer shell case allows asimpler, more inexpensive configuration.

The present invention is not limited only to the embodiment describedabove or the embodiment illustrated in the drawings, and a variety ofchanges or extensions can be made thereto.

A multi-rotation detection configuration in which the number ofrotations and the angle of rotation of the shaft 10 a are simultaneouslydetected may be employed. In this case, for example, the shaft 10 a isprovided with a reduction gear, and a counter is incremented wheneverthe shaft 10 a rotates to count the number of rotations. Also in themulti-rotation-detection-type rotation-detecting apparatus 10, theelectronic cam function and the speed limit detection function describedabove may be provided, and the angle of rotation θ associated with thecam switch signal and the setting of a predetermined threshold of ameasured number of rotations per predetermined period may be changed viathe field bus 19 a by the external apparatus described above.

As a result, quick response in the electronic cam function, easy settingof the ON/OFF timing unlike a mechanical cam, and other advantageouseffects provided in the embodiment described above can be provided.Further, in the speed limit detection function, the controller 17measures the number of rotations per the predetermined period on thebasis of the detection signal described above and outputs a switchsignal that turns on and off in accordance with a result of thecomparison between the measured number of rotations and a predeterminedthreshold. The calculation of the rotational speed can therefore beperformed in an extremely simple, precise manner. Further, high-speedON/OFF control can be performed independently, for example, of anetwork, whereby construction of a reliable system and otheradvantageous effects provided in the embodiment described above can beprovided.

Further, when the multi-rotation detection configuration, in which anabsolute position within one rotation is detected as the angle ofrotation or the absolute position is detected along with a number ofrotations, is employed, the operation efficiency of facilities to whichit is applied can be improved, as compared with a type in which arelative position is detected.

The invention claimed is:
 1. A rotation-detecting apparatus, comprising:a rotor and stators; a rotor coil disposed in the rotor; detection coilsdisposed in each of the stators; a control circuit that processesdetection signals induced in the detection coils when the rotor coil isexcited with an excitation signal to detect a relative angle of rotationbetween the rotor and the stators; and a communication unit for datacommunication with an external apparatus, wherein the communication unitis connected to the external apparatus via a cable, and the controlcircuit has a function of outputting a switch signal that turns on andoff at a preset angle of rotation based on the detection signals and isconfigured to allow the external apparatus to change a setting of theangle of rotation associated with the switch signal via thecommunication unit.
 2. The rotation-detecting apparatus according toclaim 1, further comprising an outer shell case that accommodates therotor, the stators, and a substrate of the control circuit.
 3. Therotation-detecting apparatus according to claim 2, wherein therotation-detecting apparatus has a multi-rotation detectionconfiguration in which an absolute position within one rotation isdetected as the angle of rotation or the absolute position is detectedalong with a number of rotations.
 4. The rotation-detecting apparatusaccording to claim 1, wherein the rotation-detecting apparatus has amulti-rotation detection configuration in which an absolute positionwithin one rotation is detected as the angle of rotation or the absoluteposition is detected along with a number of rotations.
 5. Arotation-detecting apparatus comprising: a rotor and stators; a rotorcoil disposed in the rotor; detection coils disposed in each of thestators; a control circuit that processes detection signals induced inthe detection coils when the rotor coil is excited with an excitationsignal to detect a relative angle of rotation between the rotor and thestators; and a communication unit for data communication with anexternal apparatus, wherein the communication unit is connected to theexternal apparatus via a cable, and the control circuit has a speedlimit detection function of measuring an angle of rotation per apredetermined period based on the detection signals and outputting aswitch signal that turns on and off in accordance with a result ofcomparison between the measured angle of rotation and a predeterminedthreshold and is configured to allow the external apparatus to change asetting of the predetermined threshold associated with the measuredangle of rotation per the predetermined period via the communicationunit.
 6. The rotation-detecting apparatus according to claim 5, furthercomprising an outer shell case that accommodates the rotor, the stators,and a substrate of the control circuit.
 7. The rotation-detectingapparatus according to claim 6, wherein the rotation-detecting apparatushas a multi-rotation detection configuration in which an absoluteposition within one rotation is detected as the angle of rotation or theabsolute position is detected along with a number of rotations.
 8. Therotation-detecting apparatus according to claim 5, wherein therotation-detecting apparatus has a multi-rotation detectionconfiguration in which an absolute position within one rotation isdetected as the angle of rotation or the absolute position is detectedalong with a number of rotations.